Fix contributing guide to reflect preferred position on indentation

call to_s on value passed to table_name=

AssetTagHelper improvements

Fix incorrect recommendation from indenting after private/protected to not.

Based on opinions of @spastorino, @jonleighton, @tenderlove

https://github.com/rails/rails/pull/1838#issuecomment-1440281
https://en.twitter.com/#!/spastorino/status/142054749351575552
https://en.twitter.com/#!/tenderlove/status/142014046445641728
https://en.twitter.com/#!/jonleighton/status/142021813415841794

another value has been specified).

allow to pass multiple sources to audio/video tags without using array

Refactored class methods on address render test

Deprecate DateTime.local_offset

This reverts commit fce92fd8.

Reason: We want any config that goes into the guides to be 100% right
and I'm not entirely sure that this one is it. We already had a similar
config that was removed in
https://github.com/rails/rails/commit/b1c20e37eccdfab7bb94d34f249c5e49256b9980

Replaced unwanted method and added to accessor for getter history

no need in separate MiniTest modules

Test for unicode path support

remove ruby 1.8 related code

Action View number helpers improvements

Also add around save to creating/updating callbacks order, and fix save
example with no validation

Use ActiveModel::Errors in inflection example docs as well.

Also fixes wrong information and link to locale file related to
Errors#full_messages in I18n guide.

Modify video_tag a bit and make audio_tag able to accept multiple sources

The methods validate_on_create and validate_on_update are not available
anymore in Rails, this removes them from the guide and adds an example
on how to use validate with the :on option.

Handle nil in add_index :length option in MySQL

Our schema.rb is being generated with an `add_index` line similar to this:

    add_index "foo", ["foo", "bar"], :name => "xxx", :length => {"foo"=>8, "bar=>nil}

This is the same as it was on Rails 3.1.3, however, now when that
schema.rb is evaluated, its generating bad SQL in MySQL:

    Mysql::Error: You have an error in your SQL syntax; check the manual
    that corresponds to your MySQL server version for the right syntax
    to use near '))' at line 1: CREATE UNIQUE INDEX
    `xxx` ON `foo` (`foo`(8), `bar`())

This commit adds a check for nil on the length attribute to prevent the
empty parens from being output.

Signed-off-by: NJosé Valim <jose.valim@gmail.com>